1. Field of the Invention
This invention relates to improved compositions and methods for the treatment and prevention of acne, and the promotion of clear skin.
2. Description of Related Art
This invention relates primarily to methods and compositions for the treatment of acne vulgaris. Acne is the most common pustular condition of the skin, disfiguring afflicted persons with inflammatory and noninflammatory lesions (including pustules, papules and comedones) during the active phase, and with atrophic scars afterwards. It occurs most commonly in teenagers, but is not confined to adolescents, as increasing numbers of persons aged >20 years are seeking advice on treatment for acne (Brogden, R. N., and Goa, K. L., Drugs, 1997, 53 511–519; this reference and others cited below are hereby incorporated herein in their entireties by reference). Although acne is generally considered to be self-limiting, its social effects can be substantial, and it may have its most severe effects on the psyche (ibid). In about 60% of teenagers, disease severity and embarrassment are sufficient for them to self-medicate with proprietary preparations and/or seek medical advice.
Acne is a multifactorial disease affecting the pilosebaceous units of the skin. Each unit consists of a large, multilobed sebaceous gland, a rudimentary hair and a wide follicular canal lined with stratefied squamous epithelium. They are found over most of the body surface but are largest and most numerous on the face, chest, and upper back. Normally, desquamated follicular cells are carried to the surface by the flow of sebum. Under the abnormal circumstances of acne vulgaris, an abnormal desquamination process provokes increased sloughing of the epithelium, which becomes more cohesive because of defective keratinization. This process causes blockage of the follicular orifice with accumulation of dead cells. Androgen stimulates the undifferentiated hormonally responsive cells making up the outer layer of the sebaceous gland lobule to divide and differentiate. Sebum production favors proliferation of the anaerobe Propionibacterium acnes, which is a normal commensal to the pilosebaceous unit, which can elicit hypersensitivity responses in acne.
The basic lesion of acne is the microcomedo. Accumulation of sebum and keratinous debris results in a visible closed comedo, or whitehead, and its continued distension causes an open comedo, or blackhead. The dark color of blackheads is due to oxidized melanin. Blackheads and microcysts are noninflammatory lesions of acne, but some comedones evolve into inflammatory papules, pustules, or nodules, and can become chronic granulomatous lesions. The initial inflammatory cell in an acute acne papule is the CD4+T lumphocyte. Duct rupture is not a prerequisite for inflammation, which is due to the release of pro-inflammatory substances from the duct. When inflammation develops, neutrophil chemotaxis occurs. These neutrophils secrete hydrolytic enzymes that cause further damage and increased permeability of the follicular wall. In pustules, neutrophils are present much earlier. More persistent lesions exhibit granulomatous histology that can lead to scarring.
The aims of treating acne are to minimize the number and severity of lesions, prevent scarring, limit disease duration, and reduce the social and psychological stress that affects many patients, particularly teenagers. Conventional treatment is directed at correcting the three major factors that seem to cause acne: (1) androgenic stimulation of the sebaceous glands and increased sebum production; (2) abnormal keratinization and impaction in the pilosebaceous canal causing obstruction to sebum flow; and (3) proliferation of P. acnes. Thus, topical agents that remove comedones, such as topical retinoids are particularly effective because they normalize desquamination within the follicular orifice, which allows the sebum to flow freely onto the surface of the skin; adalpalene, tretinoin, and tazarotene have been shown to have efficacy in treating mild to moderate acne, but all three have reported to have skin-irritating side effects including erythema, pruritis, burning/stinging, and scaling/flaking (Physicians' Desk Reference®, 56th ed. 2002, p. 2523, hereinafter referred to as “PDR”). The side effects of retinoid use are so extreme that many individuals cannot tolerate topical application of these agents at all.
Salicylic acid and benzoyl peroxide have been used to treat acne for some time. Both agents dry the skin, which helps in acne management, but they cause some skin irritation in perilesional skin areas of acne patients, especially patients with sensitive skin, and in some cases the erythema is extreme. Moreover, it has been recently reported that benzoyl peroxide seems to induce free radical production that can produce skin changes that qualitatively resemble ultraviolet B damage, e.g., increases in epidermal thickness, and deleterious changes in elastin and glycosaminoglycan content (Ibbotson, S. H., et al., J. Inves. Derm., 1999, 112: 933–938). Topical and oral antibiotics (especially tetracycline, erythromycin, and clindamycin) are sometimes prescribed for patients with inflammatory papules and pustules, but, in addition to the undesirability of antibiotic overuse in general, which can lead to enhanced susceptibility to infection, disadvantages to such treatments include phototoxicity and interactions with other medications. Other factors that play a role in exacerbating acne, including oil-based cosmetics and some drugs (e.g., androgenic hormones, high-progestin birth control pills, systemic corticosteroids, and iodide- and bromide-containing agents) are often minimized during acne treatment.
Human sebum contains an unusual mixture of lipids, with the major lipid classes being triacylglycerides (TAG, conventional fat, ≈40 to 60%), wax esters (≈19 to 26%), and squalene (≈11 to 15%), but at least 15 different neutral and polar lipids have been identified in human sebaceous gland tissue (Downie, M. M. T., and Kealey, T., J. Invest Derm., 1998, 111: 199–205). Recent studies have shown that people with acne have abnormal sebum secretions in that the ratios of essential fatty acids in sebaceous triacylglycerides (TAG, conventional fat) are skewed, as are the proportions of TAG, squalene and wax esters. It has been hypothesized that the viscosity and irritant level of these substances contribute to sebum obstruction and rupture of pilosebaceous units observed in acne. Lipogenesis in human sebaceous glands varies depending upon the metabolic state of the cells, glandular fluctuations, and the presence or absence of different substrates or other substances effecting competitition between sterol and TAG pathways (Downie and Kealey, cited above). It would be desirable to utilize this biochemical information to devise alternate treatments for acne.
It would be desirable to treat and prevent acne vulgaris manifested by the symptoms of pustule, papule, and comedone formation described above, minimizing the number and severity of lesions. It would also be desirable to provide a homogeneous skin complexion, while simultaneously reducing pore size, evening out skin texture, minimizing scar formation, treating acneform scars left after resolution of the active phase, promoting clear and firm skin tone, and providing a healthier look. It would also be desirable to have topical compositions that are effective in ameliorating skin irritation caused by conventional acne formulations so that more efficacious therapies can be devised for individual patients based on their different medical needs, including therapies that combine different treatments.